Every now and then people ask whether it is appropriate to leave a (phd, postdoc, tenure-track...) position they have accepted for a better one that became available later, or in any case how to behave when multiple positions have incompatible deadlines. The last example is Swap Postdoc position . Other older examples are Is it OK to turn down a postdoc offer (contract not signed yet) after getting a better postdoc offer, Postdoc positions: turning down alternative offers safely and timely, Tenure-track offer with other applications in progress .
This would suggest to write a "canonical question" on the subject. On the other hand, I am not so sure that a general answer exists --- maybe all these questions have peculiarities that require them to be answered on an individual basis. What do you think about it?
(I am not asking this because I wish to write myself the canonical question and answer -- on the contrary, I don't think I am experienced enough to answer this.)